In the fields of biochemistry and analytical chemistry, laboratory researchers generally prepare, manipulate, and analyze a multitude of samples for a variety of reasons. More recently, advances in scientific research and technology has exponentially increased the number of samples researchers can analyze. Many laboratories now employ sophisticated, automated machines able to prepare or analyze hundreds of samples at a time. Fields such as drug analysis now require unattended, automated analysis of many samples in an array as part of their standard instrumentation.
Chromatography systems often utilize a needle arm controlled by a user-defined program to analyze an array of samples in a tray. The needle arm forces the needle downward to pierce the septum or seal of a sample vial lid in the array. The needle draws in the sample and delivers it to a column. The needle must therefore have sufficient strength to repeatedly pierce sample seals and seal with injection ports.
Metal needles, however, are not desirable as “wetted” materials. Among other reasons, in order to increase reproducibility and eliminate errors, it is desirable to eliminate reactive interference by the needle material with the sample. In high-performance liquid chromatography (HPLC) applications, the metal can become corroded or interact with samples thereby diminishing system performance. Therefore, inert materials are desirable but are generally too soft to pierce a septum and cannot be used to form a needle.
One approach to this problem has been to use a strong metal to pierce the septum and a second inert material to aspirate the sample. An exemplar of this approach is the micro-autosampler described in U.S. Pat. No. 5,814,742 to Vissers et al. The Vissers autosampler discloses a sharpened metal needle and an intake tube positioned therein. In operation and use, the needle pierces a septum and the PEEK inner tube reciprocates from within the needle into the sample. The intake tube is composed of PEEK or fused silica. The metal needle has high strength and fatigue resistance, and the use of a PEEK intake tube prevents interaction between the metal and sample fluid in the needle. Although the metal needle does not directly contact the sample, the metal needle is introduced to the sample environment and vapors upon piercing the seal. Additionally, the second step of reciprocating the intake tube within the needle adds to the overall complexity of the system.
The Vissers autosampler needle also presents a problem when delivering sample fluid to an injection port. The PEEK inner tube lacks the strength to seal to an injection port. Either the stainless steel needle must be configured to seal to the port directly or an additional interface member must be utilized. This creates further complications and additional parts. It also may allow for the undesirable introduction of metal to the system if the port cannot accept the reciprocating intake tube.
Another approach has been to coat a stainless steel needle with an inert tetrafluoroethylene coating. Teflon coatings, however, may still degrade and wear off with time. With coatings, the sample may be exposed to the metal as it is drawn into the inner diameter of the needle. Furthermore, the coating may not adequately coat the needle and may be generally uneven. Uneven spots in the coating can lead to exposure of metal to the sample environment. Coated needles also need to be replaced periodically because the coatings tend to degrade and wear off with repeated use.
What is needed is a sampling needle which overcomes the above and other disadvantages. In particular, what is needed is a sampling needle with inert surfaces on the inner diameter (ID) and outer diameter (OD) of the needle able to withstand repeated use and having sufficient strength to pierce septa and seal to injection ports.